bluebird (n.)

also blue-bird, North American warbler-like bird, 1680s, from blue (adj.1) in reference to the chief color of its plumage + bird (n.1). Figurative use in bluebird of happiness is from 1909 play romance "l'Oiseau bleu," literally "The Blue Bird," by Belgian dramatist and poet Maurice Maeterlinck (1862-1949).